The Specific Aims are: 1)To determine the temporo-spatial localization of expression of mspry2 and to compare it with the respective temporo-spatial distribution of mspry1, 3, and 4 as well as with that of key FGF ligands (7 and 10), key FGF receptors (FGF-R2), and key effectors (phosphorylated MAPK) in early embryonic mouse lung morphogenesis; 2) To determine the respective functional specificity of mspry2&4 to negatively modulate mouse respiratory morphogenesis; 3) To determine whether mspry2 functions as an FGF ligand protein or binds candidate signaling proteins in the Ras pathway, and to determine which domains of mspry2 mediate these specific protein-protein functional interactions using mutational analysis; 4) To identify transcriptional control elements regulating spatial localization of mspry2 during lung branching morphogenesis.